What is Asphalt?

What is Asphalt?

Bitumen is a dark brown complex mixture of hydrocarbons of different molecular weights and their non-metallic derivatives, a kind of high viscosity organic liquid, mostly in liquid or semi-solid petroleum form, with a black surface, soluble in carbon disulfide, carbon tetrachloride. Bitumen is a waterproof moisture and corrosion resistant organic cementitious materials. Bitumen can be divided into three main types: coal tar pitch, petroleum asphalt and natural asphalt: of which, coal tar pitch is a by-product of coke refining. Petroleum asphalt is the residue after distillation of crude oil. Natural asphalt, on the other hand, is stored in the ground, some of which form mineral layers or accumulate on the surface of the earth's crust. Bitumen is mainly used in industries such as paints, plastics and rubber, as well as in paving.

Composition

According to the explanation of colloidal structure, with the decrease of saturated fraction and aromatic fraction of dispersing medium, the increase of protective substance gel and asphaltene content of dispersed phase, the asphalt is changed from sol-gel structure to sol-gel structure or even gel structure. The degree of penetration in the technical index of asphalt decreases and the softening point increases. When the ratio of the content of each component in the asphalt is coordinated, the best ductility can be obtained. But the above law only applies to the same oil source and the same process to obtain asphalt such as Table 1 in the asphalt are Daqing crude oil, using propyl alcohol process to obtain asphalt for the same crude oil, using different processes, or different crude oil with the same process or even different crude oil and the process of obtaining asphalt, even if they have a similar content of asphalt components, but their technical properties of the indexes can be a great deal of difference. The reason for these phenomena is due to different oil sources and processes to obtain the asphalt, although their chemical components can be very close, but the chemical structure of their components are not the same, the solubility of the components of different parameters. That is, the components of the phase solubility is different, thus forming a different colloidal structure, so their technical properties are not the same.

Solubility: hydrophobic material, it is impermeable to water, almost insoluble in water, acetone, ether, dilute ethanol, soluble in carbon disulfide, carbon tetrachloride, sodium hydroxide.　Health Hazards: Moderately toxic. Bitumen and its fumes are irritating to the skin and mucous membranes, phototoxic and carcinogenic. China's three main asphalt toxicity: coal tar pitch > shale asphalt > petroleum asphalt, the first two are carcinogenic. The main skin damage of asphalt are: phototoxic dermatitis, lesions are limited to the face, neck and other exposed parts; melanosis, lesions are often symmetrically distributed in the exposed parts of the flaky, brown - dark brown - brown-black; occupational acne; warty redundancy and accidents caused by thermal burns. In addition, there are systemic symptoms such as dizziness, head swelling, headache, chest tightness, fatigue, nausea, loss of appetite and irritation of eyes, nose and throat.

Applications

In civil engineering, asphalt is widely used in waterproofing and anticorrosion materials, mainly used in roofing, ground, underground structure of waterproofing, wood, steel corrosion. Asphalt is also widely used in road engineering pavement structure binder material, it can be built into different structures of asphalt driveway with different compositions of mineral materials in proportion.

Petroleum Asphalt

Definition

Petroleum asphalt is a product of crude oil processing, at room temperature is a black or dark brown viscous liquid, semi-solid or solid, mainly containing hydrocarbons soluble in chloroform and non-hydrocarbon derivatives, its properties and composition with the source of crude oil and production methods vary. The main components of petroleum asphalt is oil, resin and asphaltene. It also contains 2% to 3% of asphaltene carbon and carbonaceous material, also contains wax. The oil and resin in the asphalt can moisten the asphaltene. The structure of the asphalt as the core of the ground asphaltene, adsorption of part of the resin and oil, constituting a colloid.

Product Performance

Petroleum asphalt is black in color and glossy, with high temperature sensitivity. Petroleum asphalt can be categorized according to the following systems:

Production methods

(1) Distillation: the crude oil is often pressure distillation of gasoline, kerosene, diesel and other light fractions, and then by decompression distillation (residual pressure 10 ~ 100mmHg) out of the decompression distillate oil, the remaining residue in line with the specifications of road asphalt can be produced directly out of the asphalt products, the resulting asphalt is also known as straight-run asphalt, the production of road asphalt is the main method of asphalt.

(2) Solvent Precipitation: non-polar low molecular alkane solvent on the decompression of the components in the residual oil has a different solubility, the use of solubility differences can be realized component separation, and thus can be removed from the decompression of the residual oil on the asphalt properties of the components are not conducive to the production of asphalt products to meet the specifications of the requirements of the solvent precipitation method.

(3) Oxidation Method: is in a certain range of high temperature to decompression slag oil or de-oiled asphalt blown into the air, so that its composition and performance changes, the resulting product is called oxidized asphalt. Decompression slag oil at high temperatures and blowing air will produce vaporization and evaporation, while dehydrogenation, oxidation, polymerization and condensation and a series of reactions. This is a multi-component interaction of a very complex integrated reaction process, rather than just an oxidation reaction, but customarily known as the oxidation method and oxidized asphalt, also known as air blowing method and air blowing asphalt.

(4) Blending Method: blending method for the production of asphalt initially refers to the same crude oil constitutes the asphalt of the four components according to the quality requirements of the required proportion of re-blending, the resulting product is called synthetic asphalt or reconstruction of asphalt. With the development of process technology, the source of blending components have been expanded. For example, from the same crude oil or different crude oil residues or components of primary and secondary processing, as well as a variety of industrial waste oil as a blending component, which reduces the asphalt production in the choice of oil source dependence. With the growing shortage of crude oil suitable for the manufacture of asphalt, blending law shows the flexibility and economy is increasingly valued and commonly used.

(5) Emulsification Method: asphalt and water surface tension difference is very large, at room temperature or high temperature are not miscible with each other. But when the asphalt by high-speed centrifugation, shear, pounding and other mechanical effects, so that it becomes a particle size of 0.1 ~ 5 microns of particles, and dispersed into the water medium containing surfactants (emulsifiers - stabilizers), due to the emulsifier can be directed to adsorb on the surface of the asphalt particles, and thus reduces the interfacial tension of the water and asphalt, so that the asphalt particles can form a stable dispersion system in water, so that the asphalt particles in the water. Water to form a stable dispersion system, which is the oil-in-water emulsion. This dispersion system was tea brown, asphalt for the dispersed phase, water for the continuous phase, at room temperature with good mobility. In a sense, emulsified asphalt is water to "cutback bitumen", thus improving the fluidity of asphalt.

(6) Modified Asphalt: modern highways and roads have undergone many changes: traffic flow and driving frequency has increased dramatically, the axle weight of freight cars continue to increase, the general implementation of one-way traffic lane, the requirements to further improve the pavement resistance to mobility, that is, high temperature rutting resistance; improve flexibility and elasticity, that is, low-temperature resistance to cracking ability; improve the wear-resistant ability and prolong the service life. Modern buildings commonly use large-span prestressed roof panels, requiring roof waterproofing materials to adapt to large displacements, more resistant to severe high and low temperature climate conditions, better durability, self-adhesive, easy to construct, and reduce maintenance workload. These changes in the use of the environment pose a serious challenge to the performance of petroleum asphalt. Modification of petroleum asphalt to make it adapt to the above demanding requirements, has attracted attention. After decades of research and development, there have been many varieties of modified road asphalt, waterproofing membranes and coatings, showing a certain degree of engineering effectiveness. However, in view of the modified material prices are usually 2 to 7 times higher than ordinary petroleum asphalt, the user has not been able to fully grasp the engineering performance of the material, modified asphalt production growth is slow. Modified road asphalt is mainly used for airport runways, waterproof bridge decks, parking lots, sports stadiums, heavy traffic surfaces, intersections and pavement turns and other special occasions of paving applications. Europe will be modified asphalt applied to the maintenance and reinforcement of the highway network, a greater impetus to the general application of modified road asphalt. Modified asphalt waterproofing membranes and coatings are mainly used for high-grade waterproofing projects. With the progress of science and technology and the development of economic construction, will further promote the development of varieties of modified asphalt and the development of production technology. Modified asphalt varieties and preparation technology depends on the type of modifier, the amount of modifier and matrix asphalt (i.e., raw asphalt) composition and nature. Because of the many varieties of modifiers, different forms, in order to make it with petroleum asphalt to form a uniform material for engineering purposes, over the years to evaluate the various types of modifiers, and develop the corresponding formulations and preparation methods, but most of the modified asphalt has been practical engineering belongs to the patented technology and patented products.

Main uses

The main use is as infrastructure materials, raw materials and fuel, applications such as transportation (roads, railroads, aviation, etc.), construction, agriculture, water conservancy projects, industry (extractive industry, manufacturing), civil and other sectors.

Packaging and storage

Bitumen in the production and use of the process may need to be stored in the tank insulation, if handled properly, asphalt can be repeated heating can be maintained at higher temperatures for a longer period of time without serious damage to its performance. However, if the exposure to oxygen, light and excessive heat will cause the hardening of asphalt, the most significant sign is the softening point of asphalt rose, the needle penetration decreased, poor ductility, so that the use of asphalt performance loss.